Smart cards are typically wallet-sized plastic members having one or more embedded integrated circuit dies. The die of a smart card may be a microprocessor and/or one or more memory chips. A relatively few contact sites are needed to connect the smart card to a device for operating the card. Applications for a smart card include banking, security and access, and the storage of business or medical records.
In the manufacture of a smart card, a conventional technique is to form an electronic module separate from the card body to which the module is later attached. The module may include a frame comprising an underlayer of conductive material that is segmented to provide the contacts for operating the module. The underlayer is attached to a dielectric layer having areas that are punched out to expose the conductive underlayer. The die itself may be mounted in one of the exposed areas. Smaller exposed areas allow passage of wire bonds from contact pads of the die. Each wire bond electrically connects the die to one of the contact segments of the conductive underlayer. A dielectric material is then used to overcoat the die and the wire bonds, reducing the likelihood that handling will damage the module.
A number of difficulties arise from forming the electronic module in the manner described above. The most commonly used overcoat materials undergo shrinkage following curing. The shrinkage leaves a noticeable curve in the module. Automated pick-and-place equipment used in attaching modules to card bodies may have some difficulty in handling the curved modules. Because the module is flexible, wire bonds are not as reliable as other methods of providing input/output interconnections to the integrated circuit die. Moreover, wire bonds are often longer than interconnection pads of other connection schemes, adding resistance and reducing the speed of processing.
An alternative to separately fabricating electronic modules and card bodies is described in U.S. Pat No. 4,889,980 to Hara et al. A laminated card body is employed, with interior layers of the card having holes for a wiring substrate and an integrated circuit die. The outside layers of the card are entirely flat to completely enclose the wiring substrate and die. Projections of terminals are pressed through the upper layer to contact the wiring substrate for operation of the die. While Hara et al. overcome some of the difficulties described above, the multi-layered card may introduce other processing difficulties. Moreover, in many applications it is desirable to mass produce the electronic modules separately from the cards, so that an end-user can choose a unique card surface and any logos to be used on such a surface of the card.
It is an object of the present invention to provide a method of assembling a chip module for attachment to a card, wherein the module is reliably manufactured with a small number of fabrication steps and without aid of the card to which the chip module is to be attached.